Processing apparatus for gasgenerating compositions



June 11, 19 J. N. GODFREY 3,387,329

PROCESSING APPARATUS FOR GAS-GENERATING COMPOSITIONS Original Filed Oct. 20, 1965- I Ii I l i 9 I! 94 I I I \i 12 I Q I h I r I i I I; I! I I '5 I 2' i I 2 I! 9C I /0 k lac N i l I I I I I I I .43 I I I l I r Luv-l4 A l l I I 5 I l I I I- I I I m L. l 'I I I I I INVENTOR JOHN IV. 600F195) ATTORNEY United States Patent 3,387,329 PROCESSING APPARATUS FOR GAS- GENERATING (IQMPGSITEONS John N. Godfrey, Alexandria, Va., assignor to The Susquehanna Corporation, a corporation of Delaware Original application Oct. 20, 1965, Ser. No. 498,780, now

Patent No. 3,359,350, dated Dec. 19, 1967. Divided and this application Mar. 9, 1967, Ser. No. 646,772

2 Claims. (Cl. 1812) This application is a division of my application, Ser. No. 498,780, now Patent No. 3,359,350.

This invention relates to methods and apparatus for aligning elongated metallic heat conductors within a viscous propellant matrix and for making solid propellant grains containing discontinuous, elongated metallic heat conductors longitudinally aligned in the direction of flame propagation of the grain.

The incorporation of elongated metallic heat conductors in solid propellant grains is known to effect substantial increases in the mass-burning rate of the grains. A detailed discussion of the use of elongated metallic conductors is given in United States Patents 3,109,374, issued to Rumbel et al. dated Nov. 5, 1963; 3,109,375, issued to Rumbel et al. dated Nov. 5, 1963; 3,116,692, issued to Rumbel et a1. dated Jan. 7, 1964; and United States patent application Ser. No. 337,955, filed by Dale A. Madden, J an. 15, 1964 and copending herewith.

As disclosed in the aforementioned patents, the maximum increase in propellant burning rate is obtained when the elongated metallic heat conductors are longitudinally aligned in the direction of flame propagation of the grain.

Discontinuous, short, elongated metallic heat conductors can be economically incorporated into propellant compositions by conventional mixing techniques. Discontinuous heat conductors thus incorporated are, however, disposed in irregular orientation within the propellant grain and maximum burning rates are not obtained. Furthermore, variations in orientation of the discontinuous conductors throughout the length of the grain often result in non-uniform linear burning rates.

Until now, satisfactory techniques have not been available for longitudinally aligning discontinuous heat conductors within viscous propellant matrices to produce solid propellant grains having maximum burning rates.

Processes known to the plastics industry for aligning particles within a plastic mass to provide reinforcement or decorative etfects have not proven satisfactory for propellant processing. For example, such methods as illustrated by United States Patents Nos. 1,700,208; 2,682,081; 1,918,848; 2,332,829; and 2,149,066, produce orientation of particles in a plastic mass by passing the plastic mass through reduced diameter die openings or through openings in plates positioned in the flow path of the mass. The particles which contact the walls defining such openings are aligned longitudinally in the direction of flow by a stroking effect. Longitudinal alignment of particles not contacting the walls is accomplished only if the mass is of such low viscosity that substantial laminar flow, that is, an increasing gradient in flow velocity from the walls to the center of the mass, is induced by passage through the opening. Since many propellant matrices are highly viscous and move through such openings in substantially plug flow, e.g. uniform cross sectional flow rates, only limited orientation of particles within the matrices is obtainable by such methods. Furthermore, in such methods the flow path is significantly obstructed by the die or perforated plate and areas of stagnation are induced in the flowing mass. Prolonged exposure of stagnated areas of many propellant compositions to the temperature and pressure conditions of extrusion and casting operations creates hazards of explosion, decomposition and premature hardening.

The need for a satisfactory method of aligning discontinuous elongated metallic heat conductors in a viscous propellant matrix to produce propellant grains having maximum burning rates is, therefore, readily apparent.

Accordingly, it is an object of this invention to provide methods and apparatus for longitudinally aligning discontinuous elongated metallic heat conductors within a viscous propellant matrix. Another object of this invention is to provide methods for making inhibited solid propellant grains containing such heat conductors longitudinally aligned in the direction of flame propagation of the grain. Other objects and advantages of this invention will be apparent from the drawings and the following detailed description.

Referring to the drawings:

FIGURE 1 is an illustration, partly broken away, of an apparatus for aligning elongated, discontinuous, metallic heat conductors.

FIGURE 2 is a longitudinal sectional view of the apparatus shown in FIGURE 1 wherein the orientation of particles according to this invention is schematically illustrated.

FIGURE 3 is an illustration, partly broken away, of an alignment apparatus employing alternate embodiments of alignment means.

FIGURES 4, 5, 6, and 7 are longitudinal views, partly in section illustrating the production of inhibited propellant grains according to this invention.

It has been discovered that discontinuous, elongated, metallic heat conductors can be longitudinally aligned in a propellant matrix by effecting relative motion between a matrix and a plurality of alignment means disposed in a containment means. FIGURE 1 illustrates an apparatus utilized in the practice of the invention. The use of this apparatus is illustrated in FIGURE 2 wherein a viscous propellant matrix 5 containing short wire heat conductors 6 is forced through containment means comprising a passageway 1 which is serially transversed along its length by alignment means 2, 3, and 4 each comprising parallel elongated members 2a, 3a, and 4a respectively. It is seen that the wires in the matrix are disposed in random distribution above alignment means 2 and become progressively longitudinally aligned in a direction more nearly parallel to the longitudinal axis as they pass successive alignment means.

Alignment of the Wires is accomplished by contact with the elongated members of the alignment means and/or by laminar fiow patterns induced in the matrix by the'elongated members. When a wire contacts an elongated member, the force of the moving matrix turns the wire about the point of contact into a direction more nearly parallel to the longitudinal axis of the passageway. Additionally, the alignment means induces regions of laminar flow even in highly viscous compositions that would normally approach plug flow patterns.

it is seen that each alignment means defines channels in the passagewav and that the boundaries of the channels defined by different alignment means are not longitudinally colinear. That is, longitudinal planes subtending the different alignment means are laterally and/or angularly displaced from each other. Thus, the elongated members 3a are positioned to be cont-acted by wires which did not contact elongated members 2a. Also, the elongated members 3a induce additional regions of laminar flow to effect alignment of wires which do not actually contact the elongated members-In addition, wires already partially aligned by preceding alignment means are further aligned intoa direction more nearly parallel to the longitudinal axis of the passageway by the successive alignment means.

The containment means can be, for example, a passageway as described above or a stationary container such as a propellant grain mold or inhibitor beaker in which the alignment means is movable relative to the walls of the mold or beaker and any matrix disposed therein. The containment means can be of any desired cross-sectional design. The cross-sectional dimensions preferably are substantially uniform along the length of the containment means wherein the alignment means are disposed so that areas of stagnation are not induced in the flowing propellant matrix.

The alignment means of this invention are transverse to the longitudinal axis of the containment means and define channels through which the matrix passes or which are passed through the matrix. It is necessary that the channels have a transverse dimension at least equal to the longest distance subtending any heat conductor adjacent to the alignment means in order to prevent entrapment of the heat conductors and channel obstruction or blocking. To effect additional alignment by additional alignment means it is necessary that the boundaries of channels defined by the additional alignment means not be longitudinally colinear with the boundaries of channels defined by previous alignment means through which the matrix is moved.

The alignment means of this invention preferably comprise at least one elongated member transversing the longitudinal axis of the containment means. Elongated members of alignment means may be arranged in a variety of patterns. For example, the elongated members in each alignment means may be arranged in a substantially parallel non-intersecting relationship as illustrated in FIGURE 1. Alternatively as shown in FIG- URE 3 alignment means 7 consists of an elongated memher 7:: in the form of a spiral and alignment means 8 is formed by elongated members 8a arranged in the form of a screen. Other arrangements of elongated mem bers to form alignment means within the spirit of this invention will be readily apparent.

Preferably the elongated members will be relatively narrow in order to prevent stagnation of propellant flow. Generally narrow, elongated wires or strips are excellently suited for use as components of alignment means. If the matrix is very viscous and additional strength is required of the elongated members of alignment means; thin elongated bands having their widths orientated substantially parallel to the longitudinal axis of the containment means may be advantageously utilized. The elongated members of different alignment means are caused to define different channels in the containment means by varying the spacing or arrangement of elongated members of different alignment means or by directing the members of different means across the containment means at varying radial angles.

The use of alignment means comprising elongated members arranged in non-intersecting relationship as shown in FIGURE 1 minimizes blocking problems since there are no corners to trap the heat conductors. Such an arrangement is, therefore, particularly preferred.

If only one alignment means, defining channels having transverse dimensions sufficiently large to prevent blocking, is utilized, uniform alignment of heat conductors across the cross-section of the grain is not obtained. Instead, the heat conductors are preferentially aligned only in zones corresponding to longitudinal planes defined by the boundaries of the channels and along the perimeter of the grain due to contact with and/ or laminar flow patterns created by the walls of the containment means. Conductors in other zones in the cross-sectional area of the grain retain substantially random orientation. The burning of such grains proceeds more rapidly in the zones of conductor alignment and the burning surface recesses along such zones until an equilibrium point is reached. The time required to achieve such equilibrium is undesirably long when only the few zones of alignment produced by a single alignment means are present in the grain. Also, variations in alignment of conductors in zones of random orientation hinder the production of grains having reproducible burning characteristics. Therefore, to obtain grains having maximum burning rates and reproducible burning characteristics, the use of a plurality of alignment means is required.

It is often desirable that propellant grains be provided with inhibitor casings in order to restrict the burning of the propellant grain to desired surfaces.

To produce heat-conductor containing inhibited grains conveniently and economically, it is necessary to load the propellant matrix containing aligned heat conductors into the inhibitor casing without disturbing the orientation of the heat conductors. This may be accomplished as shown in FIGURE 4. An inhibitor casing 9, attached to a heat plate It is positioned around a longitudinal passageway 1 containing alignment means. As the propellant matrix is forced through the passageway and alignment means, the inhibitor casing 9 and head plate 10 are simultaneously displaced with respect to the alignment means and passageway to the position indicated by dotted line 11. The displacement is effected at about the rate at which the propellant matrix enters the inhibitor casing. Thus, there is substantially no relative motion between the inhibitor casing and the propellant matrix which would serve to disorient the aligned staples.

The matrix is cured or hardened within the encasement in such a manner as to effect an intimate bond between the hardened propellant grain and the inhibitor casing. This generally can be accomplished by curing the matrix within the insulating encasement under pressure.

In order to provide structural support and/ or dimensional stability to the inhibitor casing during the loading or hardening step of the process, it may be desirable to position a mold 12 around the inhibitor casing 9a as shown in FIGURE 5, in which case the mold and inhibitor casing are simultaneously displaced to the position indicated by dotted line 13. Alternatively, the insulating encasement 9b can be displaced into the position indicated by dotted line 14 into a stationary mold 12a as shown in FIGURE 6. If the inhibitor casing is formed of flexible material, the inhibitor casing may be inverted over a mold 1212 as shown in FIGURE 7. When the propellant matrix is forced into the inhibitor casing 90 the casing will be reinverted and forced into the position shown by dotted line 15.

The inhibitor casing may be formed of natural or synthetic polymers which may, if desired, be reinforced with fibers, wires, fabrics or the like. A wide variety of inhibitor casings and materials and methods suitable for making the same are Well-known in the propellant art, and accordingly, no attempt will be made to give a detailed discussion of inhibitor casings in this application. However, a particularly preferred propellant grain made according to this invention utilizes a combustion-restricting casing such as disclosed in Alvist V. Rice, Myron G. De- Fries and Roland C. Webster, United States patent appl cation Ser. No. 370,954, filed May 28, 1964, and copending herewith. The inhibitor casing described therein comprises an inhibitor sleeve formed of elastic material. The sleeve has restraining means embedded therein to provide a preferential direction of elasticity of the sleeve. Preferably the sleeve is restrained so as to inhibit stretch in the longitudinal direction While permitting relatively free stretch in the radial direction of the sleeve. Such an inhibitor casing having an internal dimension equal to that of the internal dimension of the passageway can be stretched over a passageway as in FIGURES 5 and 6, or a mold as in FIGURE 7; and its elastic properties will return it to an internal dimension substantially the same as the internal dimension of the passageway when the loading process forces the encasement from the passageway or mold. Thus, relative motion between the propellant matrix and the inhibitor casing is further minimized. Furthermore, hardening a propellant matrix contained within such an inhibitor casing in a grain mold under pressure expands the casing to conform to the mold thereby providing a propellant grain whose dimensions are as accurate as those of the mold.

The elongated heat conductors can be made of any heat conducting material suitable for eifecting improved performance of gas-generating compositions. For example, staples, e.g. thin flat metal strips, or short wires of aluminum, magnesium, beryllium, zirconium, titanium, silver, copper or alloys thereof can be effectively employed. If desired, such conductors can be coated with a self-oxidant composition having a higher burning rate than the gasgenerating matrix to provide gas-generating compositions having even higher burning rates than are obtainable with uncoated conductors. Alternatively, the conductors can be coated with non-self-oxidant compositions having substantially lower heat conductivity than the elongated conductors to provide gas-generating compositions having burning rates intermediate the rate of a non-conductor containing composition and a composition containing uncoated conductors. A more detailed discussion of coated and uncoated heat conductors is found in aforementioned United States Patent Nos. 3,116,692; 3,109,374; 3,109,- 375; and United States patent application Ser. No. 337,- 955 filed Jan. 15, 1964, and copending herewith.

The size of the heat conductors is determined by consideration of desired performance characteristics of the propellant. The maximum length of the heat conductors is limited only by the size of the passageway and by techniques of mixing conductors into the matrix. Generally, the conductor length should be no greater than one-half the internal diameter of the passageway. Since breakage of longer conductors may occur during mixing, a conductor length of less than 2 inches is preferred and a length of /2 inch or less is particularly preferred.

The following examples are presented to further illustrate the invention.

Example 1 A viscous propellant matrix having the following composition was prepared:

Percent Polybutadiene binder 12 Burning rate catalyst 2 Ammonium perchlorate Aluminum powder Elongated aluminum heat conductors (average size .05 in. .002 in. .0008 in.)

Pressure, Burning rate of strand cut Burning rate of strand cut; p.s.i.a. in orientation direction, in arm-orientation direcin.lsec. tion, in./sec.

Thus it is seen that the process in effective to orient the heat conductors sufficiently to provide significant increases in burning rate.

Example 2 A propellant mix having approximately the following formulation was prepared:

'Percent Carboxy terminated polybutadiene binder 10' Ammonium perchlorate 72 Burning rate catalyst 4 Aluminum powder 11.5 Elongated aluminum heat conductors as described in Example 1 2.5

v Eadial angular rotation Right bias with respect Alignment means with respect to preceding to preceding alignment alignment means, degrees means, inch 0 Ma 0 lat Strands were cut from one of the above-described grains in longitudinal and transverse directions. At about 2000 p.s.i.g. the longitudinal strands burned at an average rate of about 4.2 inches per second as compared to an average burning rate of about 2.7 inches per second for strands cut in the transverse direction. Thus, it is seen that heat conductor alignment in the longitudinal direction and improved burning rates were effected by the procedure.

The apparatus of this invention'has been described and exemplified for use in orientation of elongated heat conductors in gas-generating compositions in view of its particular advantages in this "application. However, it will be apparent that the apparatus is inherently suited for orienting of elongated particles in any viscous matrix to provide, for example, product-s having improved strength, appearance, or conductivity.

I claim:

1. An apparatus for aligning elongated metallic heat conductors within a viscous, combustible, gas-generating matrix, said apparatus comprising in combination a passageway having a plurality of alignment means serially disposed therein transversely to the longitudinal axis thereof, each of said alignment means being spaced from other alignment means along the longitudinal axis of said passageway, each of said alignment means comprising a plurality of substantially parallel elongated members, said members being separated by a distance sufiicient to permit passage of said heat conductors, and the elongated members of each of said alignment means being radially angul'arly displaced from the elongated members of other of said alignment means thereby defining channels in said passageway having boundaries not longitudinally colinear with the boundaries of channels defined by other alignment means.

2. An apparatus for aligning elongated particles within a viscous matrix, said apparatus comprising in combination a passageway having a plurality of alignment means serially disposed therein trnsversely to the longitudinal axis thereof, each of said alignment mean-s being spaced from other alignment means along the longitudinal axis of said passageway, each of said alignment means comprising a plurality of substantially parallel elongated members, said members being separated by a distance'sufficient to permit passage of said elongated particles, and the elongated members of each of said alignment means being radially angularly displaced from the elongated members of other of said alignment means thereby defining channels in said passageway having boundaries not longitudinally coline'ar with the boundaries of channels defined by other alignment means.

References Cited UNITED STATES PATENTS 1,245,898 11/1917 Gates. 2,242,364 5/ 1941 Montanari. 2,682,081 6/1954 Fisch. 2,779,972 2/ 1957 Kins. 3,344,215 9/1967 Witz et al.

FOREIGN PATENTS 1,127,140 12/1956 France.

873,140 7/1949 Germany.

WILLIAM J. STEPHENSON, Primary Examiner. 

1. AN APPARATUS FOR ALIGNING ELONGATED METALLIC HEAT CONDUCTORS WITHIN A VISCOUS, COMBUSTIBLE, GAS-GENERATING MATRIX, SAID APPARATUS COMPRISING IN COMBINATION A PASSAGEWAY HAVING A PLURALITY OF ALIGNMENT MEANS SERIALLY DISPOSED THEREIN TRANSVERSELY TO THE LONGITUDINAL AXIS THEREOF, EACH OF SAID ALIGNMENT MEANS BEING SPACED FROM OTHER ALIGNMENT MENS ALONG THE LONGITUDINAL AXIS OF SAID PASSAGEWAY, EACH OF SAID ALIGNMENT MEANS COMPRISING A PLURALITY OF SUBSTANTIALLY PARALLEL ELONGATED MEMBERS, SAID MEMBERS BEING SEPARATED BY A DISTANCE SUFFICIENT TO PERMIT PASSAGE OF SAID HEAT CONDUCTORS, ANS THE ELONGATED MEMBERS OF EACH OF ASID ALIGNMENT MEANS BEING RADIALLY ANGULARLY DISPLACED FROM THE ELOGATED MEMBERS OF OTHER OF SAID ALIGNMENT MEANS THEREBY DEFINING CHANNELS IN SAID PASSAWAY HAVING BOUNDARIES NOT LONGITUDINALLY COLINEAR WITH THE BOUNDARIES OF CHANNELS DEFINED BY OTHER ALIGNMENT MEANS. 